Hydrocarbon cracking with mixture of zeolites Y and ZSM-5

ABSTRACT

A hydrocarbon cracking catalyst comprises an ultrastable Y-type crystalline zeolite, a small pore crystalline ZSM-type zeolite, an inorganic oxide matrix and, optionally, a porous inert component. The cracking catalyst has a high activity and selectivity for the production of high octane naphtha fractions from higher boiling point hydrocarbonaceous oils. Catalytic cracking processes utilizing the catalyst are also provided.

This is a division, of application Ser. No. 044,394, filed May 31, 1979,now U.S. Pat. No. 4,239,654.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hydrocarbon cracking catalysts and usesthereof in catalytic cracking processes.

2. Description of the Prior Art

Hydrocarbon cracking catalysts comprising a zeolite dispersed in asiliceous matrix are known. See, for example, U.S. Pat. No. 3,140,249and U.S. Pat. No. 3,352,796.

U.S. Pat. No. 4,137,152 discloses a cracking process utilizing a mixtureof faujasite and mordenite.

U.S. Pat. No. 3,894,934 discloses catalytic cracking of hydrocarbonsutilizing a large pore zeolite and a small pore zeolite such as zeoliteZSM-5. These zeolites may be dispersed in a common matrix.

U.S. Pat. No. 3,871,993 discloses a process for upgrading the octanevalue of naphtha utilizing a shape selective catalyst such as zeoliteZSM-5, ZSM-11, ZSM-12, ZSM-21, mordenite, etc., in the absence of addedhydrogen.

U.S. Pat. No. 3,702,886 discloses use of ZSM-5 zeolite alone or incombination with other materials such as zeolites or inert materials forcatalytic cracking of hydrocarbons, see particularly columns 6 and 7.

U.S. Pat. No. 3,804,747 discloses a hydrocarbon conversion processutilizing a mixture of zeolites X and Y.

U.S. Pat. No. 3,758,403 discloses catalytic cracking comprising a largepore zeolite, such as zeolite Y, and a small pore zeolite, such asZSM-5, in a siliceous matrix. The matrix may be active or inactive, suchas silica-alumina or alumina. The use of the ZSM-5 type zeolite resultsin obtaining a fuel of increased octane number.

U.S. Pat. No. 3,769,202 discloses a combination catalyst comprising amixture of two different zeolites, one having a pore size greater than 8Angstroms and the other having a pore size of less than 7 Angstroms. Thezeolites are mixed with an inorganic oxide matrix such assilica-alumina. The catalyst is suitable for cracking and hydrocrackingof the hydrocarbons.

U.S. Pat. No. 3,925,195 discloses a cracking process utilizing acatalyst comprising a mixture of rare earth hydrogen Y-type zeolite, andhydrogen or transition metal exchanged mordenite, calcium exchanged typeA zeolite, or hydrogen exchanged erionite and an amorphous matrix.

U.S. Pat. No. 3,764,520 discloses a catalyst comprising a mixture of twodifferent zeolites, one having a pore size within the range of 6 to 15Angstroms and the other having a pore size of less than 6 Angstroms incombination with an inorganic oxide support. The catalyst is useful forhydrocarbon conversion processes to give increased selectivity.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided:

(a) an ultrastable Y-type crystalline aluminosilicate zeolite havingless than about 1 weight percent rare earth metals, calculated as theelemental metal, based on the zeolite;

(b) a ZSM-type zeolite; and

(c) a catalytic inorganic oxide matrix.

In one embodiment of the invention the catalyst additionally comprises aporous inorganic oxide having specific physical characteristics.

Furthermore, in accordance with the invention there is provided, acatalytic cracking process utilizing the above-stated catalyst.

DETAILED DESCRIPTION OF THE INVENTION ULTRASTABLE Y-TYPE ZEOLITECOMPONENT

"Stabilized" or ultrastable Y-type zeolites are well known. They aredescribed, for example, in U.S. Pat. Nos. 3,293,192 and 3,402,996 andthe publication, Society of Chemical Engineering (London) MonographMolecular Sieves, page 186 L (1968) by C. V. McDaniel and P. K. Maher,the teachings of which are hereby incorporated by reference. In general,"ultrastable" refers to Y-type zeolite which is highly resistant todegradation of crystallinity by high temperature and steam treatment andis characterized by a R₂ O content (wherein R is Na, K or any otheralkali metal ion) of less than 4 weight percent, preferably less than 1weight percent, and a unit cell size less than 24.5 Angstroms and asilica to alumina mole ratio in the range of 3.5 to 7 or higher. Theultrastable form of Y-type zeolite is obtained primarily by asubstantial reduction of the alkali metal ions and the unit cell sizereduction. The ultrastable zeolite is identified both by the smallerunit cell and the low alkali metal content in the crystal structure.

As is generally known, the ultrastable form of the Y-type zeolite can beprepared by successively base exchanging a Y-type zeolite with anaqueous solution of an ammonium salt, such as ammonium nitrate, untilthe alkali metal content of the Y-type zeolite is reduced to less than 4weight percent. The base exchanged zeolite is then calcined at atemperature of 1000° F. to 1500° F. for up to several hours, cooled andthereafter again successively base exchanged with an aqueous solution ofan ammonium salt until the alkali metal content is reduced to less than1 weight percent, followed by washing and calcination again at atemperature of 1000° to 1500° F. to produce an ultrastable zeolite Y.The sequence of ion exchange and heat treatment results in thesubstantial reduction of the alkali metal content of the originalzeolite and results in a unit cell shrinkage which is believed to leadto the ultra high stability of the resulting Y-type zeolite. Theparticle size of the zeolites is usually in the range of 0.1 to 10microns, more particularly in the range of 0.5 to 3 microns. For use inthe present invention, the ultrastable Y-type zeolite components of thecatalyst will be substantially free of rare earth metals such as forexample cerium, lanthanum, praseodymium, neodymium, promethium,samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,yttrium, thulium, scandium, lutecium and mixtures thereof. By"substantially rare earth free" is meant that the rare earth metalcontent of the zeolite will be less than about 1 weight percent,calculated as the elemental metal based on the zeolite. Similarly smallamounts (1 weight percent) of magnesium or calcium ions may be exchangedinto the zeolite.

Suitable amounts of the ultrastable Y-type zeolite in the catalyst ofthe present invention include from about 0.1 to about 40 weight percent,preferably from about 5 to about 25 weight percent, based on the totalcatalyst.

THE SMALL PORE ZEOLITE COMPONENT

Suitable small pore zeolites are the zeolites of the type designated"ZSM" by Mobil, particularly ZSM-5 type zeolites such as those describedin U.S. Pat. No. 3,702,886 and in Nature 272, pages 437-438, Mar. 30,1978.

The ZSM-5 type zeolites are shape selective for adsorption of normal andmethyl substituted paraffins and are known to be effective to cracknormal and slightly branched paraffins.

The original cations of the small pore zeolites can be replaced by ionexchange by methods well known in the art. Part or all of the originalcations can be replaced by tetraalkyl ammonium cations, metal ions,ammonium ions and hydrogen ions. More preferably, the hydrogen form ofthe small pore zeolite component of the catalyst of the presentinvention is used. Suitable weight ratio of ultrastable Y-zeolite tosmall pore zeolite ranges from about 1:1 to 20:1.

THE INORGANIC OXIDE GEL MATRIX

Inorganic oxide gels suitable as components of the catalyst of thepresent invention are amorphous catalytic inorganic oxides such assilica, silica-alumina, silica-zirconia, silica-magnesia, alumina-boria,alumina-titania and the like, and mixtures thereof. Preferably, theinorganic oxide gel is a silica-containing gel, more preferably theinorganic oxide gel is an amorphous silica-alumina component such as aconventional silica-alumina cracking catalyst, several types andcompositions of which are commercially available. These materials aregenerally prepared as a cogel of silica and alumina or as aluminaprecipitated on a preformed and preaged silica hydrogel. In general,silica is present as the major component in the catalytic solids presentin such gel, being present in amounts ranging from about 55 to about 100weight percent, preferably silica will be present in amounts rangingfrom about 70 to 90 weight percent. Particularly preferred are twocogels, one comprising about 75 weight percent silica and 25 weightpercent alumina and the other comprising from about 87 weight percentsilica and 13 weight percent alumina. The inorganic oxide gel componentmay suitably be present in the catalyst of the present invention inamounts ranging from about 40 to about 90 weight percent, preferablyfrom about 55 to about 75 weight percent, based on the total catalyst.

THE POROUS INERT COMPONENT

Optionally, a porous inert inorganic oxide may be used as component inthe catalyst of the present invention.

The porous inert inorganic oxide component of the catalyst of thepresent invention may be present in the finished catalyst in amountsranging from about 5 to about 35 weight percent, preferably from about10 to about 30 weight percent, based on the total catalyst. The inertporous component can be chosen from a wide variety of solid porouscatalytically inert materials. The term "catalytically inert" isintended herein to designate that the porous material has substantiallyno catalytic cracking activity or has less catalytic cracking activitythan the inorganic oxide gel component of the catalyst.

Preferably, the inert material will be a bulk material. The term "bulk"with reference to the porous material is intended herein to designate amaterial which has been preformed and placed in a physical form suchthat its surface area and pore structure is stabilized so that when itis added to an impure inorganic gel containing considerable amounts ofresidual soluble salts, the salts will not alter the surface and porecharacteristics appreciably, nor will they promote chemical attack onthe preformed inert material which could then undergo change. Forexample, addition of "bulk" alumina will mean a material which has beenformed by suitable chemical reaction, the slurry of hydrous aluminaaged, filtered, dried, washed free of residual salts and then heated toreduce its volatile content to less than about 15 weight percent. Ifdesired, the washed, aged hydrous alumina filter cake can be reslurriedwith water and used in making the composite catalyst. The resultinginert material is suitable for use as the porous inert material of thepresent invention. Suitable materials for use as inert material in thecatalyst of the present invention include alumina, titania, zirconia,magnesia and mixtures thereof. Preferably, the porous material is a bulkalumina which may additionally be stabilized with from about 0.5 toabout 6 weight percent silica. Alumina stabilized with silica iscommercially available. A preferred inert porous material for use ascomponent of the catalyst is one having initially, after heating at1000° F. in air for six hours, a surface area greater than about 20square meters per gram (BET method-Brunauer, Emmett and Teller, see VanNostrand Chemist's Dictionary 1953 edition), preferably greater than 100m² /g, preferably at least 200 m² /g and a pore volume greater thanabout 0.25 cubic centimeter per gram. Desirably, the inert porousmaterial has at least 0.2 cubic centimeters per gram pore volume in thepores having diameters ranging from about 90 to about 200 Angstroms.These stated physical characteristics are those of the porous inertmaterial when taken separately after calcining 6 hours at 1000° F. andprior to being composited with the other components.

Alternatively and optionally, an alumina hydrosol or hydrogel or hydrousalumina slurry may be used, provided that the ultimate porous inertcomponent, when dried and calcined separately has physicalcharacteristics within the above stated ranges.

The catalysts of the present invention may be prepared by any one ofseveral methods. The preferred method of preparing one of the catalystsof the present invention, that is, a catalyst comprising silica-aluminaand as porous inert material, alumina, is to react sodium silicate witha solution of aluminum sulfate to form a silica/alumina hydrogel slurrywhich is then aged to give the desired pore properties, filtered toremove a considerable amount of the extraneous and undesired sodium andsulfate ions and then reslurried in water. Separately, a bulk aluminamay be prepared, for example, by reacting solutions of sodium aluminateand aluminum sulfate, under suitable conditions, ageing the slurry togive the desired pore properties to the alumina, filtering, drying,reslurrying in water to remove sodium and sulfate ions and drying toreduce volatile matter content to less than 15 weight percent. Thealumina is then slurried in water and blended, in proper amount, withthe slurry of impure silica/alumina hydrogel.

The zeolites are added to this blend. A sufficient amount of eachcomponent is utilized to give the desired final composition. Theresulting mixtures may be filtered to remove a portion of the remainingextraneous soluble salts therefrom. The filtered mixture is then driedto produce dried solids. The dried solids are subsequently reslurried inwater and washed substantially free of the undesired soluble salts. Thecatalyst is then dried to a residual water content of less than about 15weight percent.

The catalyst of the present invention is suitable for catalyticcracking. Catalytic cracking with the catalyst of the present inventioncan be conducted in any of the conventional catalytic cracking manners.Suitable catalytic cracking conditions include a temperature rangingfrom about 750° to about 1300° F. and at a pressure ranging from aboutatmospheric to about 100 psig, typically from about atmospheric to about20 psig. The catalytic cracking process may be carried out as a fixedbed, moving bed, ebullating bed, slurry, transferline (disperse phase)or fluidized bed operation. The catalyst of the present invention isespecially suitable for use in a fluidized bed and transferlinecatalytic cracking process. The catalyst may be regenerated atconditions which include a temperature in the range of about 1100° F. toabout 1500° F., preferably from about 1175° F. to about 1350° F.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples are presented to illustrate the presentinvention.

EXAMPLE 1

This example describes the preparation of catalysts. Their crackingperformance is described in a subsequent example.

Catalyst A is a commercially used catalyst believed to comprise about 16weight percent of rare earth-containing Y-type faujasite, about 28weight percent kaolin and about 56 weight percent silica-alumina gelmatrix. The final catalyst comprises about 2.9 weight percent rare earthmetal oxides, based on the total catalyst. Catalyst A is a catalyst ofreference.

Catalyst B is also a catalyst of reference. It was made as follows:

(a) a dilute sodium silicate solution (about 5 weight percent SiO₂) wasgelled by admixing with CO₂ under pressure, ageing the gel to give thedesired pore properties, admixing with aluminum sulfate solution andadjusting the pH of the impure gel to about 5 to 5.5;

(b) the gel is admixed with a slurry of ultrastable Y faujasite crystalsand then a slurry of bulk alumina stabilized with about 2.5 weightpercent silica. The composite slurry was colloid milled twice to assurehomogeneity and spray dried;

(c) The material was washed with ammonium sulfate solution to removeextraneous soluble salts, rinsed with H₂ O and dried. The catalystcomprised about 20 weight percent ultrastable Y-type faujasite, 20weight percent alumina and 60 weight percent silica-alumina gel.

Catalyst C, which is a catalyst in accordance with the presentinvention, was made in a manner similar to catalyst B except that instep (b), the gel was admixed with a mixed slurry of ultrastable Yzeolite and a zeolite similar to the zeolite described in the literatureas ZSM-5. The overall preparation procedure was the same as for catalystB. Catalyst C comprises about 18 weight percent ultrastable Y-typezeolite, 2 weight percent of a ZSM-5 type zeolite, 20 weight percentbulk alumina and 60 weight percent silica-alumina gel.

Catalyst D, which is a catalyst in accordance with the presentinvention, was made in a similar manner to catalyst C except that therelative proportions of ultrastable Y-type faujasite and ZSM-5 typezeolite were changed. Catalyst D comprised about 15 weight percentultrastable Y-type zeolite, 5 weight percent of a ZSM-5 type zeolite, 20weight percent bulk alumina stabilized with silica and 60 weight percentsilica-alumina gel.

EXAMPLE 2

This example compares the cracking performance and the cracked productqualities of the catalysts of the present invention, namely, catalysts Cand D, with the reference catalysts A and B. Catalysts A, B, C and Dwere each calcined at 1000° F. for 6 hours and then steamed at 1400° F.and 0 psig pressure for 16 hours. The catalysts were evaluated forcracking activity in a standard microactivity test. The results aresummarized in Table I. The catalysts were also evaluated for crackingperformance in a full cycle cracking operation. The unit is acirculating fluidized catalytic cracking unit with a regenerator andreactor/stripper vessels. It is operated once-through, that is, there isno recycle oil mixed with fresh feed. Reactor temperature was 925° F.and regenerator temperature was 1105° F. The feedstock was 560° to 1050°F. boiling range (at atmospheric pressure) vacuum gas oil. The unit wasoperated at a constant catalyst to oil weight ratio of 4. The results ofone set of tests utilizing catalysts A, B and D are summarized in TableI. The catalysts were compared at a constant 70 volume percentconversion (430° F.⁻ ). The results show that reference catalyst B andcatalyst D, which is a catalyst in accordance with the presentinvention, each gives substantially higher activity and superior octanenumber C₅ /430° F. naphtha relative to the commercial reference catalystA. Furthermore, use of the higher C₃ and C₄ olefins products as feed toan alkylation unit would result in a substantial net increase in totalnaphtha yield for both catalysts B and D relative to catalyst A.Comparing catalyst D with reference catalyst B (which has the samecomponents except for the ZSM-5 type zeolite), it can be seen that theaddition of the ZSM-5 type zeolite to the catalyst resulted in asubstantial increase in naphtha octane numbers. It is to be noted thatthe increase in motor octane is greater than the increase in researchoctane. Furthermore, when potential alkylate is combined with C₅ /430°F. cracked naphtha, a substantially higher total naphtha yield isobtainable with catalyst D, which is a catalyst in accordance with thepresent invention.

                  TABLE I                                                         ______________________________________                                        Catalyst          A        B        D                                         ______________________________________                                        MAT Conversion.sup.3                                                                            69       73.5     76.7                                      Yields & Product                                                              Qualities @ 70% Conversion                                                    H.sub.2, wt. %    0.056    0.062    0.042                                     C.sub.3.sup.- dry gas, wt. %                                                                    5.6      6.4      8.1                                       Total C.sub.4, vol %                                                                            13.1     11.8     16.9                                      Coke, wt. %       3.5      2.7      3.0                                       C.sub.5 /430 Naphtha, Vol. %                                                                    60.5     62       55                                        RONC.sup.1        90.8     93.8     95.2                                      MONC.sup.2        79.8     80.5     83.1                                       ##STR1##         85.3     87.2     89.2                                      C.sub.3.sup.=, vol. %                                                                           3.7      4.4      6.3                                       C.sub.4.sup.=, vol. %                                                                           6.8      7.6      11.3                                      C.sub.5 /430 + Alk., vol. %                                                                     82.0     87.0     91.4                                      ______________________________________                                         .sup.1 Research Octane Number Clear                                           .sup.2 Motor Octane Number Clear                                              .sup.3 Microactivity Test  see Oil & Gas Journal, 1966 vol. 64, pp. 7, 84     85 and Nov. 22, 1971, pp. 60-68.                                         

In a second set of experiments, catalysts B, C and D, after steaming at1400° F., were tested for cracking performance in a similar manner tothe one described above. The results are summarized in Table II. Thecatalysts were compared at a constant 65 volume percent conversion (430°F.⁻).

                  TABLE II                                                        ______________________________________                                        Catalyst          B        C        D                                         ______________________________________                                        ZSM-5 type, wt. % 0        2        5                                         USY type, wt. %   20       18       15                                        Product Yields and                                                            Qualities at 65 vol. %                                                        Conversion                                                                    H.sub.2, wt. %    0.08     0.04     0.03                                      C.sub.3 H.sub.6, wt. %                                                                          3.6      4.7      5.4                                       C.sub.4 H.sub.3 (tot), vol. %                                                                   7.0      8.4      10.6                                      Carbon, wt. %     2.5      2.0      2.5                                       C.sub.5 /430° F., vol. %                                                                 58.5     55.5     53.0                                      RON Clear         93.4     94.4     94.8                                      MON Clear         80.3     80.9     81.2                                       ##STR2##         86.8     87.7     88.0                                      C.sub.5 /430° F. + alkylate, vol. %                                                      80.3     80.3     85.9                                      ______________________________________                                    

The advantages of incorporating minor amounts of ZSM-5 type of zeoliteinto cracking catalysts comprising ultrastable Y-type faujasite, bulkalumina and silica-alumina gel are shown by higher octane number crackednaphtha and, when combined with alkylate from the cracked light olefins,a potentially substantially higher total naphtha yield. Furthermore,hydrogen yields are decreased with the catalysts of the presentinvention.

What is claimed is:
 1. A catalytic cracking process which comprisescontacting a hydrocarbonaceous feed at catalytic cracking conditions inthe absence of added hydrogen with a catalyst comprising:(a) anultrastable Y-type crystalline alumino-silicate zeolite having less thanabout 1 weight percent rare earth metals, calculated as the elementalmetal, based on the zeolite; (b) a small pore crystalline ZSM-5 typezeolite; and (c) a catalytic inorganic oxide matrix.
 2. The process ofclaim 1 wherein said catalyst additionally comprises a porous inorganicoxide having initially a surface area greater than about 20 squaremeters per gram and a pore volume greater than about 0.25 cubiccentimeter per gram.
 3. The process of claim 2 wherein said porousinorganic oxide has initially a surface area greater than about 100square meters per gram and at least 0.2 cubic centimeter per gram of itspore volume in pores having diameters ranging from 90 to 200 Angstroms.4. The process of claim 1 wherein the weight ratio of said ultrastableY-type zeolite to said small pore zeolite ranges from about 1:1 to about20:1.
 5. The process of claim 1 wherein said small pore crystallinezeolite is a ZSM-5 type zeolite.
 6. The process of claim 5 wherein saidZSM-5 type zeolite is the hydrogen form of the ZSM-5 type zeolite. 7.The process of claim 2 wherein said porous inorganic oxide is selectedfrom the group consisting of alumina, titania, zirconia, magnesia andmixtures thereof.
 8. The process of claim 2 wherein said porousinorganic oxide comprises porous alumina.
 9. The process of claim 2wherein said porous inorganic oxide comprises alumina stabilized withfrom about 0.5 to about 6 weight percent silica.
 10. The process ofclaim 1 wherein said matrix comprises silica-alumina.
 11. The process ofclaim 1 wherein said catalyst comprises from about 5 to about 40 weightpercent of said ultrastable Y-type zeolite.
 12. The process of claim 1wherein said catalytic cracking conditions include a temperature rangingfrom about 750° to 1300° F. and a pressure ranging from about 0 to 100psig.